1. Field
Apparatuses consistent with the exemplary embodiments relate to an optical apparatus such as a fluidic lens.
2. Description of the Related Art
With development of digital technologies, digital convergence is being expanded rapidly. In particular, in media and communication fields, digital convergence is most actively advancing. Representative digital convergence products are mobile communication devices. Recently, various imaging devices, such as a digital camera, a digital camcorder, and the like, as well as devices for games, music playback, broadcasting, the Internet, etc., are combined with mobile communication devices. Such imaging devices are widely installed in various mobile communication devices, such as a mobile phone, a laptop computer, a Personal Digital Assistant (PDA), etc.
Recently, in accordance with miniaturization, slimness, and popularization of mobile electronic equipment with an imaging device, a need for a small-sized, slim and low-cost imaging device is increasing. In particular, since recent mobile devices are released with various digital electronic devices (for example, a MP3 player, a video player, a DMB television, etc.) as well as an imaging device, a need for a small-sized, slim imaging device is more increasing. However, an imaging device including a focusing optical system is one type of electronic equipment that has great difficulties in reducing their size or thickness.
Initial models of mobile electronic devices with imaging devices did not require high performance of imaging devices. However, recently, in order to meet various requirements or tastes of consumers, a variety of mobile devices with imaging devices have been developed, and performance requirements for such mobile devices, such as resolution, are also increasing. For example, initial imaging devices have supported only limited functions such as a macro mode with a fixed and shortest focal distance of 60 cm, but recently developed imaging devices are supporting more various functions, including an auto focus function, a zoom function, a macro mode allowing photographing within 30 cm or less, an image stabilization function, and so on.
In order to implement the auto focus function, the zoom function, the macro mode, etc., in an imaging device, a function of adjusting the focal distance of focusing optical system is needed. As a method for varying the focal distance of focusing optics, a method of using a step motor, a method of using a Voice Coil Motor (VCM), etc., have been utilized. These methods drive a motor, etc., to change the distances between lenses of focusing optics and thus vary a focal distance. Thus, the methods have limitation in reducing the size of an image device, and also have difficulties in integrally fabricating an image device, which becomes a factor of increasing manufacturing costs.
In order to overcome these drawbacks, a method of using a fluidic lens has been suggested. A fluidic lens is a kind of optical apparatus having a structure where optical fluid is sealed up by an optical membrane. In the fluidic lens, curvature of the lens surface varies by adjusting pressure that is applied to the lens surface of the optical membrane. A representative example of such a fluidic lens is disclosed in Korean Laid-open Patent Application No. 2008-0043106, entitled “Optical Lens and Manufacturing Method thereof”, filed by the same applicant, the entire disclosure of which is incorporated herein by reference for all purposes.
Since a fluidic lens can vary a focal distance using changes in curvature of the lens surface, it is not needed to change the distances between lenses of focusing optics in order to adjust the focal distance. Accordingly, since an imaging device with a fluidic lens requires neither a step motor nor a VCM, etc., to move lenses of focusing optics, and also does not need to ensure a separate space for moving the lenses, the imaging device can be fabricated to be compact. Also, since the fluidic lens disclosed in the above-mentioned Korean Laid-open Patent Application can be fabricated in wafer level, the fluidic lens is suitable to mass production and contributes to a reduction of manufacturing costs.
Meanwhile, most of electronic equipment with a mobile device is designed to stably operate within a predetermined temperature range. The operating temperature of electronic equipment may depend on purposes or functions. Also, the operating temperature range of personal portable electronic devices is generally from about −20° C. to about 60° C. The operating temperature range is also applicable to imaging devices with fluidic lenses.
However, optical fluid used in a fluidic lens has a relatively large coefficient of thermal expansion (CTE) and accordingly, has relatively large changes in volume with respect to changes in temperature. Since the fluidic lens changes curvature of the lens surface depending on pressure that is applied to an optical membrane by the optical fluid in order to adjust a focal distance, the curvature of the lens surface, that is, the focal distance of the fluidic lens, is affected by changes in temperature. The phenomenon may prevent the fluidic lens from operating stably within a predetermined operating temperature range (for example, from −20° C. to 60° C.).